The addition of a capo allows a musician to quickly alter the pitches produced when unfingered strings are strummed. A traditional capo raises the pitch of each string by bringing all strings into contact with the selected fret. A musician may also alter the tuning of one or more strings after installation of a capo to obtain desired playing characteristics. Once affixed to an instrument, the traditional capo severely limits the selection of notes that it is possible for the instrument to produce because notes cannot be produced by the portions of the strings cut off by the capo.
U.S. Pat. No. 4,183,279 to Shabram discloses a variable chord-forming capo attached by a strap to the neck of the instrument. In operation, eccentric disks may be rotated to engage or disengage from each string. Both the Shabram partial capo and the capo disclosed in U.S. Pat. No. 4,334,457 to Spoonts appear to be somewhat time-consuming to set and adjust. Although any open string might be fingered on either side of the installed Shabram capo, neither Shabram nor Spoonts disclose features designed to facilitate fingering of strings above as well as below the capo. The size of the eccentric disks would make it difficult to position the fingers to fret strings near the Shabram capo, especially when it is desired to simultaneously fret strings both above and below the capo.
A further limitation on the types of capos disclosed by Spoonts and Shabram results from the fact that the strings of a stringed instrument are separated by distances that are neither uniform among instruments nor constant for any given instrument. Strings are often spaced farther apart at the bridge than at the nut. In order to engage the strings at any point along the neck of an instrument, a partial capo must allow transverse adjustment of the string engaging elements. The Spoonts capo provides no transverse adjustment of string engaging elements. The requirement that the Shabram string engaging elements be rotatable precludes simple interlocking string engaging element forms. A string that a musician desired to depress with the capo could instead slip into the gap between adjacent disks. Should a slightly misaligned string slip between adjacent string engaging elements during performance, it might be necessary to halt playing, remove ;the capo, re-adjust it, and re-install it.
A popular embodiment of a traditional capo is disclosed in U.S. Pat. No. 4,583,440 to Powell. A steel spring is used to bias the two arms or jaws of a clamp toward one another. Powell discloses a stepped underside for the string engaging portion of the upper clamp member for allowing the capo to be used on a five-string banjo. U.S. Pat. No. 5,431,080 to Wiesenthal discloses a capo that has many of the functional and convenience features of the Powell capo, such as being operable with one hand. However, Wiesenthal uses a cam instead of a spring to bias the string engaging member toward the fretboard.
U.S. Pat. No. 4,195,546 to Urbank discloses a chord selector that could effect some of the functionality of a partial capo. However, the Urbank device can be used to bring strings into contact with only frets that are close to the nut. Because the string-depressing arms disclosed by Urbank extend above each string from the head of the instrument to the contacted fret, it would be difficult for a musician to finger strings adjacent to the chord-forming arms of the Urbank invention. In recent years, guitars have become increasingly popular among musicians. As more people have developed an interest in making music with the guitar, interest in advanced techniques for tuning and playing has also grown. One explanation of the growing interest in technique is that musicians need to perform at a higher standard than ever before because low levels of skill are less acceptable among audiences that have become accustomed to musical excellence as the result of the widespread availability of high quality recorded music. By proper use of a capo, musicians may be able to execute musical performances that they would otherwise be unable to accomplish. Forming certain bar chords might, for example, be beyond the abilities of a musician. Using a capo could make it possible for that person to play such chords.
A partial capo, by engaging fewer than all strings with a selected fret, enables a musician to form chords and sequences of notes that would be difficult or impossible to play otherwise. A partial capo allows a musician to easily set and play drone notes on instruments other than the five-string banjo. In order to fully exploit the potential of using a partial capo, however, it is necessary to manipulate strings on both sides of the installed capo. Previously known capos hinder the musician who wishes to engage strings with frets situated on both sides of the capo.
What is needed, then, is a capo that poses a minimal obstruction when installed on the neck of a stringed instrument. The capo needs to have a low profile in order to allow the musician's fingers to clear the capo when the hand is moved along the neck of the instrument. Moreover, adjustment of the capo bar is needed so that it extends over no more strings than necessary. The capo must be capable of engaging any combination of strings with the selected fret without over-stretching and detuning any string. Finally, it must be possible to quickly and easily configure the capo and engage the desired strings with it.